This invention relates to a reciprocating travelling shear designed to cut material by making a tool post travel reciprocatingly in parallel with the travelling material, such as pipe and sheet, and by moving the cutting tool held by the tool post vertically by a press while the tool post is travelling in the same direction as the material.
In the conventional reciprocating travelling shear, the tool post is held between a lower rail and an upper rail is made to slide along these rails. The press ram is fixed on the upper rail and one end of each of two crank arms, arranged in the extending direction of the rail, is installed on the top surface of the ram freely rotatably.
The other ends of each of these crank arms are respectively connected to gears, and between these gears is provided a drive gear engaging with both gears.
The drive shaft of the drive gear is coupled with a flywheel through a clutch and the flywheel is driven by a motor. The engagement and disengagement of the clutch is performed by pneumatic control. A friction disk brake is employed to control the rotation of the drive shaft when the clutch is disengaged. When the drive gear is rotated one turn, the upper rail makes a vertical movement through the crank arm towards the lower rail. At this time the upper blade held by the tool post also moves vertically and, in cooperation with the lower blade of the tool post, cuts the material travelling between the two blades. In other words, the machine cuts the material through press operation. In the state where the travelling speed of the material is the same as the travelling speed of the tool post and the material protrudes from the cutting tool by the set cut length, said drive gear is rotated one turn to move the upper blade vertically to cut the material to set length. As has been described so far, in the conventional reciprocating travelling shear, control of the drive gear was made by clutch and brake. The clutch was controlled pneumatically and the response speed was slow compared with the control by electric signals. Therefore, it was difficult to obtain an accurate cutting timing. The damping force of the brake is affected by ambient temperature. With the increase in the number of times of use, the temperature of friction plate rises, resulting in the unfixed stop position of the upper rail. It, therefore, is impossible to replace automatically the cutting tool during continuous operation.
Moreover, as was described before, due to both the inaccuracy in the cutting time by clutch control and the inaccuracy in the stopping position of the upper rail caused by temperature rise of the brake, if the tool post shifts from the center part of the ram and the upper rail in their extending direction, dispersion of the cutting resistance in the forward and backward directions about the center part of the upper rail becomes unbalanced. As a result, the machine fails to perform favorable cutting. Furthermore, since both the clutch and the brake have a short service life, they require frequent replacement. In view of the operation delay these two have, there is a limit in the number of times of cutting operation per unit time, making it impossible to perform high speed operation.
An object of this invention is to provide a reciprocating travelling shear in which the stop position of the upper blade is always fixed and accordingly the replacement of cutting tool can be made without delay.
Another object of this invention is to provide a reciprocating travelling shear capable of performing a cutting operation at the center part of the ram and accordingly capable of performing favorable cutting without destroying the machine and cutting tool.
Still another object of this invention is to provide a reciprocating travelling shear capable of increasing the number of cuts per unit time over that of conventional machine.
Still another object of this invention is to provide a reciprocating travelling shear which has a long service life and which generates almost no noise.